Triakshar mrtyunjaya mantra

Hello, I've read about the triakshar mrtyunjaya, which is said to be the shortest or seed form of maha mrtyunjaya.
I wanted to know if it should be pronounced "om haum joom sah" or "om haum joom saha".
I was thinking that it may be like the "namaha", which is pronounced so when ending a sentence and "namah" when used in the middle of a sentence.
So maybe those chanting the the triakshar as an opening for the further recitation (trayambakam yajamahe sugandhim etc...) use the form "sah" and those using it alone use "saha" because it ends there and then repeat.
But this is just my speculation. I'd like someone to clarify.

Thanks.